/*
 * Copyright (C) 2006 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.util.concurrent;

import static com.google.common.collect.Sets.newHashSet;

import java.util.Set;

/**
 * Emulation of AggregateFutureState.
 */
abstract class AggregateFutureState<OutputT> extends AbstractFuture.TrustedFuture<OutputT>
{
    // Lazily initialized the first time we see an exception; not released until all the input futures
    // & this future completes. Released when the future releases the reference to the running state
    private Set<Throwable> seenExceptions = null;
    private int remaining;

    AggregateFutureState(int remainingFutures)
    {
        this.remaining = remainingFutures;
    }

    final Set<Throwable> getOrInitSeenExceptions()
    {
        if (seenExceptions == null)
        {
            seenExceptions = newHashSet();
            addInitialException(seenExceptions);
        }
        return seenExceptions;
    }

    abstract void addInitialException(Set<Throwable> seen);

    final int decrementRemainingAndGet()
    {
        return --remaining;
    }

    final void clearSeenExceptions()
    {
        seenExceptions = null;
    }
}
